60+ Must-Know Node JS Interview Questions and Answers 2025 for Beginners and Professionals

Have you ever walked out of an interview wishing you had handled that one tricky question better? Preparing for Node.js interview questions can feel overwhelming—especially when interviewers expect you to juggle concepts like asynchronous programming, microservices, and cloud integrations. 

The stakes are high, and each question is a chance to showcase not just your technical know-how but your ability to think on your feet and solve real-world problems.

This guide is here to demystify the process, offering practical Node.js interview questions and answers tailored to 2025’s hiring demands. Whether it’s optimizing performance or debugging elusive errors, we’ve got you covered. Let’s tackle these challenges head-on and ensure you walk into your next interview fully prepared to succeed!

Foundational Node JS Interview Questions and Answers

This section focuses on the core concepts and foundational knowledge you need for entry-level Node.js roles. These Nodejs interview questions and answers will give you a strong foundation to start your journey.

Dive into these vital questions to set the stage for deeper Node.js knowledge.

1. What Is The Main Purpose Of Node.js?

Direct Answer: Node.js is designed to create scalable and efficient network applications. It uses an event-driven, non-blocking I/O model to handle numerous simultaneous connections, making it ideal for real-time applications like chat apps and collaborative tools.

Node.js stands out because it allows you to use JavaScript for both front-end and back-end development, streamlining workflows and enhancing consistency.

Want to dive deeper into Node JS? Kickstart your journey with upGrad’s online data science courses and gain the skills to excel in this data-driven world!  

2. How Do You Install Node.js On Your System? 

Direct Answer: You can install Node.js by downloading the installer from the official Node.js website.

Below are the steps for different platforms:

• Windows: Download the .msi file, run it, and follow the setup wizard.
• macOS: Use the .pkg installer or install it via Homebrew (brew install node).
• Linux: Install via a package manager like apt, yum, or dnf, or download the source code and compile it.

After installation, verify it by running node -v and npm -v in your terminal.

Also Read: How to Install Node.js and NPM on Windows?

3. What is npm in Node.js?

Direct Answer: npm stands for Node Package Manager. It’s a tool that comes with Node.js and helps you manage packages and dependencies in your projects.

Here are its primary uses:

• Installing libraries and tools for your application.
• Managing versioning and updates of packages.
• Creating and sharing reusable code as npm modules.

These functionalities make npm a cornerstone of Node.js development.

Also Read: Yarn vs NPM: Which Package Manager to Choose in 2024?

4. What Are The Different Types Of Modules In Node.js?

Direct Answer: Node.js supports three main types of modules:

• Core Modules: Built-in modules like http, fs, and path.
• Local Modules: Custom modules you create in your project.
• Third-party Modules: Modules installed via npm, such as express or lodash.

Below is a quick comparison:

Each type serves a specific purpose, enhancing the flexibility of Node.js.

Also Read: Node JS Versions: Which One to Download?

5. What Is A Callback Function In Node.js?

Direct Answer: A Javascript callback function is a function passed as an argument to another function, executed after the first function completes. It’s a key feature of asynchronous programming in Node.js.

Also Read: React useCallback Hook: Why, When & How to Use It?

6. How Does Node.js Handle Concurrent Requests?

Direct Answer: Node.js uses a single-threaded event loop to manage multiple simultaneous requests. This design allows it to handle thousands of connections without creating a new thread for each one, unlike traditional servers.

Here’s how it works:

• Incoming requests are added to an event queue.
• The event loop processes each request asynchronously.
• Blocking operations are delegated to worker threads.

This efficiency makes Node.js perfect for I/O-intensive tasks.

7. What Is The Event Loop In Node.js?

Direct Answer: The Event Loop is a mechanism in Node.js that manages asynchronous operations. It continuously checks the call stack and callback queue to execute tasks.

Below are its phases:

1. Timers
2. I/O callbacks
3. Idle, prepare
4. Poll
5. Check
6. Close callbacks

Also Read: Event Bubbling and Event Capturing in Javascript Explained: How to Utilize?

8. What Is The Role Of The require() Function In Node.js?

Direct Answer: The require() function is used to include modules in Node.js applications.

Example:

const fs = require('fs'); 

Here, fs is loaded and ready for use.

The function simplifies modular code, a vital feature in modern applications.

9. What Is The Difference Between Synchronous And Asynchronous Execution In Node.js?

Direct Answer: Here's a concise comparison table highlighting the key differences between synchronous and asynchronous execution in Node.js:

Node.js encourages asynchronous execution for better scalability.

Also Read: React Functional Components with Examples

10. What Is A Package Manager In Node.js?

Direct Answer: A package manager, like npm or Yarn, manages project dependencies and libraries. It simplifies the installation, updating, and removal of modules.

Node.js developers use these tools to streamline workflows and enhance productivity.

Also Read: Node JS Developer Salary in India 2024

11. What Are Streams In Node.js?

Direct Answer: Streams in Node.js are objects that enable reading and writing data piece-by-piece, rather than loading it all at once. This approach is efficient for processing large amounts of data.

Types of streams:

• Readable Streams: Used to read data (e.g., fs.createReadStream).
• Writable Streams: Used to write data (e.g., fs.createWriteStream).
• Duplex Streams: Can read and write (e.g., sockets).
• Transform Streams: Modify or transform data (e.g., compression).

Streams are an essential feature of Node.js for handling large files efficiently.

Also Read: Node JS vs Python: Difference Between Node JS and Python

12. What Is The Use of The fs Module In Node.js?

Direct Answer: The fs (File System) module in Node.js provides an API to interact with the file system.

Common uses of the fs module:

• Reading files: fs.readFile()
• Writing files: fs.writeFile()
• Deleting files: fs.unlink()
• Renaming files: fs.rename()

The fs module is often used in Node.js interview questions and answers for practical coding tests.

Also Read: How to Install FS Module in Node JS?

13. What Is A Server-Side JavaScript Environment?

Direct Answer: A server-side JavaScript environment, like Node.js, allows you to run JavaScript code on a server. This is in contrast to traditional JavaScript, which runs in a browser.

Key features of server-side JavaScript environments:

• Access to system resources like file systems and databases.
• Ability to handle HTTP requests and responses.
• Support for frameworks like Express.js for creating web applications.

This feature bridges the gap between front-end and back-end development.

Also Read: Top 7 JavaScript Frameworks to Learn in 2024

14. What Is The Significance of the ‘This’ Keyword In Node.js?

Direct Answer: In Node.js, the ‘this’ keyword refers to different objects depending on the context:

• Global Scope: Refers to the global object.
• Function Scope: Refers to the object that owns the function.
• Arrow Functions: Does not bind its own this and inherits it from the parent context.

Understanding this is crucial for answering Nodejs interview questions involving object-oriented programming.

Also Read: A Complete Guide on OOPs Concepts in Python

15. What Is A RESTful API In The Context Of Node.js?

Direct Answer: A RESTful API is an architectural style that uses HTTP requests to perform operations like GET, POST, PUT, and DELETE on resources. In Node.js, RESTful APIs are typically implemented using frameworks like Express.js.

Also Read: How to Make API Calls in Angular Applications

16. How Does Node.js Handle Memory Management?

Direct Answer: Node.js uses the V8 JavaScript engine for memory management. It automatically allocates and deallocates memory using garbage collection.

However, developers must ensure:

• Proper handling of closures and references to prevent memory leaks.
• Avoiding large objects in memory for extended periods.

Below are common memory-related tools:

• process.memoryUsage(): Provides memory usage stats.
• --inspect flag: Helps debug memory leaks.

17. What Are The Main Features Of Node.js?

Direct Answer: Node.js offers several standout features:

• Event-driven architecture: Handles multiple requests efficiently.
• Non-blocking I/O: Executes asynchronous operations.
• Cross-platform compatibility: Runs on Windows, macOS, and Linux.
• Rich library of modules: Simplifies development.
• Single programming language: Uses JavaScript for front-end and back-end.

These features make Node.js an indispensable tool for modern web development.

Also Read: Top 20 Programming Languages of the Future

18. How Does Node.js Differ From Traditional Server-Side Platforms?

Direct Answer: Here’s how Node.js differs from traditional server-side platforms.

Node.js stands out due to its event-driven, single-threaded nature, making it perfect for real-time applications.

Also Read: Top 5 Python Modules You Should Know in 2024

19. What Is The Use Of The Process Object In Node.js?

Direct Answer: The process object in Node.js provides information and control over the current Node.js process.

Key uses include:

• Accessing environment variables: process.env
• Exiting a process: process.exit()
• Listening to events: process.on('exit', callback)

This object is crucial for debugging and managing runtime behavior.

Also Read: React Native Debugging: Techniques, Tools, How to Use it?

20. What Are Environment Variables In Node.js?

Direct Answer: Environment variables in Node.js are key-value pairs used to store configuration settings and sensitive data outside the application code. They allow for easy management of different configurations for different environments, such as development, testing, and production. 

In Node.js, environment variables are accessed through process.env. They help in maintaining security, scalability, and flexibility by enabling configuration changes without modifying the codebase directly.

Also Read: Most Important Python Functions [With Examples] | Types of Functions

Intermediate Node JS Interview Questions and Answers for All Experience Levels

This section delves into intermediate-level Nodejs interview questions and answers. You’ll explore critical topics like asynchronous programming, performance optimization, core Node.js concepts, and effective problem-solving strategies. 

The questions below gradually deepen your understanding, preparing you for advanced Node.js roles.

21. What Is Middleware In Express.js?

Direct Answer: Middleware in Express.js refers to functions that execute during the lifecycle of a request and response. Middleware can modify requests, responses, or terminate the request-response cycle.

Middleware enables developers to manage complex tasks like logging, authentication, and error handling efficiently.

Also Read: Exception Hierarchy in Java: Hierarchy of Java Exception Classes

22. How Does Node.js Handle File Uploads?

Direct Answer: Node.js handles file uploads using libraries like multer or formidable. These libraries parse incoming form data and store uploaded files in a specified location.

Example: This example demonstrates a basic server setup to handle file uploads with multer.

Code Snippet:

const express = require('express');
const multer = require('multer');
const path = require('path');

const app = express();
const PORT = 3000;

// Configure multer storage
const storage = multer.diskStorage({
  destination: (req, file, cb) => {
    cb(null, './uploads');
  },
  filename: (req, file, cb) => {
    cb(null, `${Date.now()}-${file.originalname}`);
  },
});

const upload = multer({ storage });

app.post('/upload', upload.single('file'), (req, res) => {
  res.send(`File uploaded successfully: ${req.file.filename}`);
});

app.listen(PORT, () => {
  console.log(`Server running on http://localhost:${PORT}`);
});

Output:

1. Start the server and make a POST request to /upload with a file using a tool like Postman or an HTML form.
2. If the file uploads successfully, you will see a response like:

File uploaded successfully: 1672523945678-example.txt

3. The uploaded file is saved in the uploads folder.

Explanation: multer.diskStorage sets file storage and naming, upload.single('file') handles single file uploads, req.file holds file metadata, and response returns the file's name.

Also Read: Libraries in Python Explained: List of Important Libraries

23. What Is The Difference Between Promise And Callback In Node.js?

Direct Answer: Here are the differences between promise and callback.

Promises improve code readability and maintainability, addressing issues like callback hell.

Also Read: Why Learn to Code Now and How? Top 4 Reasons To Learn

24. What Is The Significance Of The __dirname Variable In Node.js?

Direct Answer: The __dirname variable in Node.js returns the absolute path of the directory containing the current script.

Example usage:

console.log(__dirname); 

This is especially useful when creating file paths dynamically.

25. How Can You Handle Exceptions In Node.js?

Direct Answer: Handle exceptions in Node.js using:

• Try-catch blocks: For synchronous code.
• Error events: For EventEmitter-based operations.
• Global exception handlers: Using process.on('uncaughtException', callback).

Also Read: Exception Handling in Java 

26. What Is The Purpose Of The Node.js Cluster Module?

Direct Answer: The Node.js cluster module is used to improve the performance and scalability of applications by enabling the creation of multiple worker processes that share the same server port. 

Key purposes:

• Load Balancing: Distributes incoming requests across multiple workers for efficient resource usage.
• Fault Tolerance: Ensures app stability by restarting crashed workers.
• Parallel Execution: Leverages multi-core processors to handle higher workloads.

Also Read: Hierarchical Clustering in Python 

27. How Do You Manage Dependencies In Node.js?

Direct Answer: Manage dependencies in Node.js using npm or Yarn. Use commands like:

• npm install <package>: Install a dependency.
• npm update: Update all dependencies.
• npm uninstall <package>: Remove a dependency.

A package.json file tracks your project’s dependencies and versions.

Also Read: Installing Dev Dependencies with npm: Beginners Guide

28. What Is The Difference Between .on() And .once() Methods In Node.js EventEmitter?

Direct Answer: Here are the differences between .on() and .once() methods.

Also Read: How to Take Multiple Input in Python: Techniques and Best Practices

29. What Is The Use Of The Util Module In Node.js?

Direct Answer: The util module in Node.js provides utility functions to simplify common programming tasks, such as debugging, formatting strings, and working with objects. 

Key uses include:

• util.format: Formats strings similar to printf in C.
• util.inspect: Debugs objects by converting them into human-readable strings.
• util.promisify: Converts callback-based functions to promise-based ones.
• util.types: Checks data types with specialized type-checking functions.  

Also Read: How to Use Axios in React 

30. How Does Node.js Handle JSON Data?

Direct Answer: Node.js handles JSON data efficiently, as it includes built-in methods to parse and stringify JSON. Here's a quick overview:

• Parse JSON: Converts a JSON string into a JavaScript object using JSON.parse().
• Stringify JSON: Converts a JavaScript object into a JSON string using JSON.stringify().
• Ideal for APIs: Commonly used to handle request and response payloads in web applications.

Also Read: An Introduction to Package JSON Scripts in Node.js

31. What Is The Purpose Of The Crypto Module In Node.js?

Direct Answer: The crypto module in Node.js provides cryptographic functionalities for secure data handling. It supports hashing, encryption, and digital signatures.

Key features of the crypto module:

• Hashing: Generate fixed-length strings from data using algorithms like SHA-256.
• Encryption/Decryption: Protect sensitive information.
• Digital Signatures: Verify data authenticity.

This module is critical for applications handling passwords, secure tokens, or sensitive user data.

Also Read: Understanding Types of Data: Why is Data Important, its 4 Types, Job Prospects, and More

32. What Is A WebSocket In Node.js?

Direct Answer: A WebSocket is a protocol enabling full-duplex, real-time communication between a server and clients. Unlike HTTP, WebSockets maintain persistent connections, eliminating the need for repeated requests.

WebSockets are widely used in chat applications, live notifications, and gaming platforms.

Also Read: What is ChatGPT? An In-Depth Exploration of OpenAI's Revolutionary AI

33. How Does Node.js Handle Concurrency With The Help Of Event Loop?

Direct Answer: Node.js uses a single-threaded Event Loop to manage concurrency efficiently. The Event Loop processes incoming requests, delegates blocking tasks (like file I/O or database queries) to worker threads, and executes callbacks when tasks are complete.

Here’s the step-by-step process:

1. Incoming requests are added to an event queue.
2. The Event Loop picks requests and processes non-blocking tasks directly.
3. Blocking tasks are assigned to the Thread Pool.
4. Once tasks are complete, their results are added to the callback queue.

This architecture ensures Node.js remains lightweight and fast, even under heavy workloads.

Also Read: Multithreading in Python

34. What Is The Purpose Of The Async/Await Pattern In Node.js?

Direct Answer: The async/await pattern in Node.js is used to simplify working with asynchronous code, making it more readable and easier to manage.

• Async Functions: Allow returning a promise.
• Await Keyword: Pauses execution until the promise resolves or rejects, simplifying the handling of asynchronous operations.
• Improved Readability: Avoids callback hell or chaining multiple .then() methods.

Also Read: Ultimate Guide to Synchronization in Java

35. What Is CORS And How Is It Handled In Node.js?

Direct Answer: CORS (Cross-Origin Resource Sharing) is a mechanism that allows or restricts resources on a web server to be accessed by a domain outside of the server's origin. This is implemented to maintain security and prevent unauthorized access.

Example: The following example demonstrates how to enable CORS in a Node.js application using the cors middleware.

Code Snippet:

// Import required modules
const express = require('express');
const cors = require('cors');

// Initialize the app
const app = express();

// Use CORS middleware
app.use(cors());

// Example route
app.get('/data', (req, res) => {
  res.json({ message: 'CORS enabled for this route!' });
});

// Start the server
app.listen(3000, () => {
  console.log('Server running on http://localhost:3000');
});

Output: When you make a request to the /data endpoint from a different origin (e.g., from a frontend app on a different port or domain), you’ll see:

{
  "message": "CORS enabled for this route!"
}

Explanation: CORS middleware with the cors package enables cross-origin requests by setting appropriate headers, customizable through options passed to app.use(cors()).

Are you ready to master JavaScript and tackle challenges like CORS handling in Node.js? upGrad's Advanced JavaScript for All course is your ultimate guide!

36. How Do You Handle Authentication In Node.js Applications?

Direct Answer: In Node.js applications, authentication can be handled using various strategies. Here's an overview:

• Session-based Authentication: Using express-session to store user information on the server side.
• Token-based Authentication (JWT): JSON Web Tokens for stateless authentication, often used in APIs.
• OAuth: Integrating third-party services (e.g., Google, Facebook) for authentication.
• Passport.js: Middleware for handling different authentication strategies, including local, OAuth, and others. 

Node.js applications often combine these techniques for robust authentication systems, especially when dealing with RESTful APIs or microservices.

Also Read: Spring Boot Annotations Everyone Should Know

37. What Is The Difference Between Express.js And Koa.js?

Direct Answer: Here’s the difference between express.js and koa.js.

Both frameworks are popular, but your choice depends on project requirements and team preferences.

Also Read: React.js vs Node.js: The Battle of JavaScript Frameworks

38. How Does Node.js Handle Request And Response Cycles In HTTP?

Direct Answer: Node.js handles request and response cycles in HTTP using its event-driven, non-blocking I/O model. Here's a short breakdown:

• Server Creation: A Node.js server is created using the http module, listening for incoming requests.
• Request Handling: When a request is received, Node.js triggers an event and processes it via callback functions.
• Response: Node.js generates an appropriate response and sends it back to the client.
• Non-blocking: Node.js processes multiple requests concurrently without blocking the event loop, making it highly efficient for I/O operations.

Also Read: Servlet Life Cycle in Java: Methods, Architecture, Comparison & Setup

39. How Can You Prevent Memory Leaks In Node.js?

Direct Answer: Prevent memory leaks by:

• Avoiding global variables.
• Cleaning up event listeners with .removeListener() or .off().
• Using tools like node-inspect or heapdump to monitor memory usage.

Memory leaks reduce application performance and reliability, making prevention crucial.

Also Read: Data Visualisation: The What, The Why, and The How!

40. What Are The Various Methods Of Deploying A Node.js Application?

Direct Answer: Deploy Node.js applications using methods like:

1. Cloud Platforms: AWS, Azure, Google Cloud.
2. Platform-as-a-Service (PaaS): Heroku, Vercel.
3. Containers: Docker and Kubernetes.
4. On-Premise Servers: Self-hosted environments with reverse proxies like Nginx.

Each deployment method offers unique benefits, allowing flexibility based on your project needs.

Also Read: AWS Vs Azure: Which Cloud Computing Platform is Right For You?

Expert-Level Node JS Interview Questions and Answers

This section delves into advanced Node.js interview questions and answers. The questions below focus on scenarios where depth and precision are key, ensuring you’re prepared to meet the toughest challenges in your Node.js journey.

41. What Is The Use Of Process.nextTick() In Node.js?

Direct Answer: The process.nextTick() method schedules a callback function to execute after the current operation completes but before any I/O events in the event loop.

It provides a way to prioritize certain operations over others. This is especially useful in scenarios requiring faster execution than I/O-bound tasks.

Also Read: Java Do While Loop With Examples

42. How Do You Perform Load Balancing In Node.js Applications?

Direct Answer: Load balancing distributes incoming requests across multiple servers or processes to optimize performance. In Node.js, you can achieve this using:

1. Cluster Module: Spawns worker processes to handle multiple requests.
2. Reverse Proxy: Tools like Nginx or HAProxy distribute traffic between servers.
3. Cloud Load Balancers: AWS Elastic Load Balancer or Google Cloud Load Balancer.

Also Read: AWS Tutorial for Beginners Is Out. Here’s What’s In

43. What Is A Worker Thread In Node.js And How Does It Differ From A Child Process?

Direct Answer: Worker threads and child processes handle concurrent tasks in Node.js, but they operate differently. Here’s how:

Worker threads are ideal for CPU-intensive tasks, while child processes suit independent workflows.

Also Read: Multithreading in C#: Benefits, Basics & Best Practices

44. Explain The Concept Of Promises In Node.js.

Direct Answer: Promises in Node.js are used to handle asynchronous operations and manage asynchronous code more efficiently than traditional callbacks.

Key Points:

• Represents a value that may not be available yet, but will be resolved in the future.
• Can be in one of three states: Pending, Resolved (Fulfilled), or Rejected.
• Provides methods like .then(), .catch(), and .finally() to handle the outcome (success or failure).
• Helps to avoid "callback hell" by chaining asynchronous tasks in a cleaner, more readable way.

Also Read: What are Promises in Angular? Syntax, Examples, Future

45. How Does Node.js Handle Streams For Handling Large Data Sets?

Direct Answer: Node.js efficiently processes large data sets using streams, which break data into manageable chunks instead of loading it all at once into memory. This approach minimizes memory usage and improves performance.

• Readable Streams: Handle input data (e.g., files, network requests).
• Writable Streams: Manage output data (e.g., writing to a file).
• Duplex Streams: Act as both readable and writable (e.g., sockets).
• Transform Streams: Modify or process data chunks as they pass through (e.g., compression).

Streams enable real-time data processing, making Node.js ideal for big data and file handling. 

Wonder how streams optimize data handling in Node.js? Master similar data techniques in upGrad’s unsupervised learning: clustering course.

46. What Are The Key Differences Between Node.js And Python For Back-End Development?

Direct Answer: Here are the differences between node.js and python.

Python is preferred for Artificial intelligence and deep learning, while Node.js excels in handling high-concurrency scenarios.

Ready to master Python for web apps and deep learning? Start your journey with upGrad’s learn basic python programming course!

47. What Is The Purpose Of The child_process Module In Node.js?

Direct Answer: The child_process module in Node.js enables the creation and management of child processes to perform tasks outside the main event loop. Its purposes include:

• Executing Shell Commands: Run system commands like ls, mkdir, etc.
• Spawning Processes: Create new processes with spawn or fork.
• Handling Asynchronous Tasks: Offload compute-heavy operations.
• Inter-process Communication (IPC): Exchange messages between processes for advanced workflows.

Also Read: How to Create Index.js File in Node?

48. How Does Node.js Handle Non-Blocking I/O Operations?

Direct Answer: Node.js handles non-blocking I/O operations using an event-driven architecture and a single-threaded event loop. Here’s how it works:

• Asynchronous APIs: Node.js uses non-blocking APIs to perform I/O tasks without waiting for them to complete.
• Event Loop: The event loop listens for events and executes callbacks when tasks finish.
• Libuv Library: Underlying C++ library libuv manages threads for heavy I/O tasks.
• Callbacks and Promises: Results are processed through callbacks, Promises, or async/await.
• Efficient Resource Usage: This design ensures scalability for high-concurrency applications.

Also Read: React useEffect() Hook: Structure, Usage, Examples & Tips

49. How Do You Implement Caching In Node.js Applications?

Direct Answer: Implement caching using libraries like redis or node-cache.

Redis Example: The following example demonstrates how to set and retrieve a key-value pair using the Redis database in a Node.js application.

Code Snippet:

// Import the Redis library
const redis = require('redis');

// Create a Redis client
const client = redis.createClient();

// Set a key-value pair in Redis
client.set('name', 'Rajesh', redis.print);

// Retrieve the value using the key
client.get('name', (err, reply) => console.log(reply));

// Close the Redis connection
client.quit();

Output:

Reply: OK
Rajesh

Explanation:

• Redis Client Initialization:

The redis.createClient() creates a connection to the Redis server.

• Setting a Key-Value Pair:

client.set('name', 'Rajesh', redis.print) stores the value 'Rajesh' with the key 'name' in Redis.

The redis.print callback logs a message (Reply: OK) to confirm the operation was successful.

• Retrieving the Value: 

client.get('name', callback) retrieves the value for the key 'name' and logs it. In this case, the output is Rajesh.

• Closing the Connection: 

client.quit() ensures the Redis client connection is properly closed after the operations are complete.

50. What Are The Types Of Testing You Can Perform On A Node.js Application?

Direct Answer: Here’s a breakdown of the various types of testing you can perform on a Node.js application to ensure its functionality, reliability, and performance:

Thorough testing ensures application reliability and performance under various conditions.

Also Read: Apache Spark Tutorial For Beginners: Learn Apache Spark With Examples

51. How Do You Debug A Node.js Application Using Node Inspector?

Direct Answer: You can debug Node.js applications using Node Inspector, a powerful debugging tool integrated with the Chrome DevTools interface.

Steps to Debug:

1. Start your Node.js application in debug mode using the --inspect flag:

node --inspect app.js  

2. Open Google Chrome and go to chrome://inspect.

3. Click on the "Inspect" link next to your application.

4. Use Chrome DevTools to set breakpoints, inspect variables, and monitor the call stack.

Debugging ensures your application behaves as expected and helps identify potential issues.

Also Read: Full Stack Developer Tools To Master In 2024

52. What Is The Difference Between EventEmitter And Observable In Node.js?

Direct Answer: Here’s a concise table highlighting the key differences between EventEmitter and Observable in Node.js.

Need clarity on EventEmitter vs. Observable? Gain hands-on experience with upGrad's React.js for beginners course.

53. How Do You Ensure High Availability In A Node.js Application?

Direct Answer:

To ensure high availability, implement the following strategies:

1. Load Balancing: Use tools like Nginx to distribute traffic.
2. Clustering: Leverage Node.js cluster module to use multiple CPU cores.
3. Health Checks: Monitor application status and restart services if needed.
4. Graceful Restarts: Implement logic to handle application restarts without downtime.

High availability minimizes disruptions and ensures consistent performance.

Also Read: Hadoop Clusters Overview: Benefits, Architecture & Components

54. What Are Microservices In Node.js, And How Do You Build Them?

Direct Answer: Microservices are small, independently deployable services that work together to form an application.

Steps to Build Microservices in Node.js:

1. Divide the Application: Split functionality into independent services.
2. Use Frameworks: Tools like Express or NestJS help develop microservices.
3. Implement Communication: Use REST APIs or messaging systems like RabbitMQ or Kafka.
4. Containerization: Use Docker for deploying microservices efficiently.

Microservices enable scalability and maintainability for large applications.

Also Read: Docker Architecture Overview & Docker Components

55. What Is The Role Of The Node.js Event Loop In Handling I/O-Bound Tasks?

Direct Answer: The Node.js event loop processes asynchronous I/O tasks without blocking the main thread.

Key Phases of the Event Loop:

1. Timers: Executes setTimeout() and setInterval() callbacks.
2. I/O Callbacks: Handles completed I/O operations.
3. Idle, Prepare: Internal operations.
4. Poll: Retrieves new I/O events.
5. Check: Executes setImmediate() callbacks.
6. Close Callbacks: Closes sockets or file descriptors.

This non-blocking mechanism allows efficient handling of high-concurrency I/O operations.

Also Read: Multithreading in Java Explained

56. How Do You Implement Rate Limiting In A Node.js API?

Direct Answer: Rate limiting controls the number of requests a user can make to an API, preventing abuse and ensuring fair usage.

Steps to Implement Rate Limiting:

1. Use express-rate-limit middleware: The following example demonstrates how to implement rate limiting in a Node.js application using the express-rate-limit middleware.

Code Snippet:

const rateLimit = require('express-rate-limit');  

const limiter = rateLimit({  
    windowMs: 15 * 60 * 1000, // 15 minutes  
    max: 100, // Limit each IP to 100 requests per window  
});  

app.use(limiter);

Output:

When you make a request to the /info endpoint for the first 100 times within 15 minutes, you’ll see:

Hello, Ravi! You are accessing a rate-limited endpoint.

2. Store request data in Redis for distributed applications.

Rate limiting enhances security and prevents server overload.

57. What Are The Security Best Practices For Node.js Applications?

Direct Answer:

Follow these best practices to secure Node.js applications:

• Sanitize Input: Prevent SQL injection or XSS attacks.
• Use HTTPS: Encrypt communication between server and clients.
• Validate Data: Check user input using libraries like Joi or Validator.js.
• Hide Sensitive Information: Store secrets in environment variables using dotenv.
• Update Dependencies: Regularly check and update dependencies using npm audit.
• Set HTTP Headers: Use helmet to configure secure headers.

Secure practices protect against vulnerabilities and maintain trust.

Also Read: How to Get List of Globally Installed Packages of NPM

Essential Node JS Coding Interview Questions to Prepare For

These coding questions challenge your ability to write efficient Node.js programs while addressing real-world scenarios. Below are practical examples and explanations to sharpen your coding expertise and excel in competitive interviews.

58. Write A Node.js Program To Create An HTTP Server That Listens On Port 3000 And Responds With A "Hello, World!" Message For Every Incoming Request.

Direct Answer: The following example demonstrates how to create a simple HTTP server in Node.js that responds with "Hello, World!" when accessed.

Code Snippet:

// Import the http module
const http = require('http');

// Create the server
const server = http.createServer((req, res) => {
    res.statusCode = 200; // Set the HTTP status code to 200 (OK)
    res.setHeader('Content-Type', 'text/plain'); // Set the response header for plain text
    res.end('Hello, World!'); // Send the response
});

// Start the server and listen on port 3000
server.listen(3000, () => {
    console.log('Server running on port 3000');
});

Output:

When you start the server and access http://localhost:3000 in your browser or make a request using tools like curl, you will see the following response:

Hello, World!

Explanation: The Node.js http module creates servers using createServer, handling requests (req) and responses (res). It sends "Hello, World!" on port 3000.

Also Read: Python Requests Module Guide: How to Use Requests Library in Python?

59. Write A Node.js Program That Reads A File Called Input.txt, Counts The Number Of Words In The File, And Writes The Word Count To A File Called Output.txt.

Direct Answer: The following example demonstrates how to count the number of words in a text file (input.txt) and save the word count to another file (output.txt) using Node.js.

Code Snippet:

const fs = require('fs');  

fs.readFile('input.txt', 'utf8', (err, data) => {  
    if (err) {  
        console.error('Error reading file:', err);  
        return;  
    }  

    const wordCount = data.split(/\s+/).length;  
    const output = `Word count: ${wordCount}`;  

    fs.writeFile('output.txt', output, (err) => {  
        if (err) {  
            console.error('Error writing file:', err);  
        } else {  
            console.log('Word count written to output.txt');  
        }  
    });  
}); 

Input (input.txt):

Namaste, my name is Priya Sharma. I live in Delhi, India.

Output (output.txt):

Word count: 10

Explanation: The code reads a text file, counts its words, and writes the count to another file, handling errors efficiently—perfect for text analysis tasks.

Also Read: Java Architecture & Components Explained

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60. Write A Node.js Program Using Express.js To Create A Basic RESTful API With The Following Endpoints:

• Get /Users: Returns A List Of Users.
• Post /Users: Accepts User Data And Adds It To The List Of Users.

Direct Answer: The following example demonstrates how to create a simple user management API using Express. It includes GET and POST routes to fetch and add user details.

Code Snippet:

// Import required modules
const express = require('express');  
const app = express();  

// Middleware to parse JSON data
app.use(express.json());  

// Dummy user data array
let users = [];  

// GET route to fetch all users
app.get('/users', (req, res) => {  
    res.json(users);  
});  

// POST route to add a new user
app.post('/users', (req, res) => {  
    const user = req.body;  
    users.push(user);  
    res.status(201).json(user);  
});  

// Start the server
app.listen(3000, () => {  
    console.log('API running on port 3000');  
});  

Output:

• GET /users response:

[]

• POST /users with request body:

{
  "name": "Amit Sharma",
  "age": 30,
  "city": "Delhi"
}

• After posting the data, GET /users will return:

[
  {
    "name": "Amit Sharma",
    "age": 30,
    "city": "Delhi"
  }
]

Explanation: The /users GET route returns all users, while the /users POST route adds a new user to an initially empty array. The server runs on port 3000.

61. Write A Node.js Program Using The ws Module To Create A WebSocket Server Where Multiple Clients Can Connect And Send Messages To Each Other In Real-Time.

Direct Answer: The following example demonstrates how to create a WebSocket server in Node.js, where messages sent by one client are broadcast to all connected clients in real-time.

Code Snippet:

// Import the WebSocket module
const WebSocket = require('ws');  

// Create a new WebSocket server that listens on port 8080
const wss = new WebSocket.Server({ port: 8080 });  

// Event listener for a new connection
wss.on('connection', (ws) => {  
    console.log('Client connected');  

    // Event listener for receiving a message from a client
    ws.on('message', (message) => {  
        console.log(`Received: ${message}`);  

        // Broadcast the message to all connected clients
        wss.clients.forEach((client) => {  
            if (client.readyState === WebSocket.OPEN) {  
                client.send(message);  
            }  
        });  
    });  

    // Event listener for when a client disconnects
    ws.on('close', () => {  
        console.log('Client disconnected');  
    });  
});  

console.log('WebSocket server running on port 8080');  

Output: When a client connects to the WebSocket server and sends a message, such as "Hello, world!", the output will be:

Client connected
Received: Hello, world!
Client disconnected

For every connected client, the message "Hello, world!" will be broadcast.

Explanation: The WebSocket server listens on port 8080, handles client connections, broadcasts received messages, and logs disconnections upon client exits.

Also Read: How to Make a Chatbot in Python Step by Step [With Source Code] in 2025

62. Write A Node.js Program Using Express.js And An In-Memory Array (Or A Simple Database Like SQLite) To Create A CRUD (Create, Read, Update, Delete) API For Managing A To-Do List.

Direct Answer: The following example demonstrates how to create a simple To-Do application using Express.js, where users can add, view, update, and delete to-dos.

Code Snippet:

// Importing required modules
const express = require('express');
const app = express();
const port = 3000;

// Middleware to parse JSON data
app.use(express.json());

// In-memory array for storing to-do items
let todos = [];

// Create a new to-do
app.post('/todos', (req, res) => {
    const { id, task, completed } = req.body;

    if (!id || !task) {
        return res.status(400).json({ error: 'ID and task are required.' });
    }

    todos.push({ id, task, completed: completed || false });
    res.status(201).json({ message: 'To-do created successfully.', todos });
});

// Read all to-dos
app.get('/todos', (req, res) => {
    res.status(200).json(todos);
});

// Read a single to-do by ID
app.get('/todos/:id', (req, res) => {
    const { id } = req.params;
    const todo = todos.find(t => t.id === id);

    if (!todo) {
        return res.status(404).json({ error: 'To-do not found.' });
    }

    res.status(200).json(todo);
});

// Update a to-do by ID
app.put('/todos/:id', (req, res) => {
    const { id } = req.params;
    const { task, completed } = req.body;
    const todo = todos.find(t => t.id === id);

    if (!todo) {
        return res.status(404).json({ error: 'To-do not found.' });
    }

    if (task) todo.task = task;
    if (typeof completed === 'boolean') todo.completed = completed;

    res.status(200).json({ message: 'To-do updated successfully.', todo });
});

// Delete a to-do by ID
app.delete('/todos/:id', (req, res) => {
    const { id } = req.params;
    const index = todos.findIndex(t => t.id === id);

    if (index === -1) {
        return res.status(404).json({ error: 'To-do not found.' });
    }

    todos.splice(index, 1);
    res.status(200).json({ message: 'To-do deleted successfully.', todos });
});

// Starting the server
app.listen(port, () => {
    console.log(`Server running at http://localhost:${port}`);
});

Output:

When you create a new to-do with the following request:

Request:

POST /todos
{
  "id": "1",
  "task": "Buy groceries",
  "completed": false
}

Response:

{
  "message": "To-do created successfully.",
  "todos": [
    { "id": "1", "task": "Buy groceries", "completed": false }
  ]
}

Similarly, a request to fetch all to-dos:

Request:

GET /todos

Response:

[
  { "id": "1", "task": "Buy groceries", "completed": false }
]

Explanation: The /todos API lets you manage to-do items: create (POST), view all (GET), fetch by ID (GET /:id), update (PUT /:id), and delete (DELETE /:id), with appropriate error handling for missing data or invalid IDs.

Also Read: Understanding CRUD Operations in ASP.NET MVC: Best Practices and Examples

Effective Tips For Acing Node JS Interviews

To succeed in a Node.js interview, it’s crucial to approach it with the right mindset. Your preparation should be thorough, aligning your knowledge with the expectations of the hiring team. 

Here are some key tips that can elevate your interview performance and help you stand out from the competition.

• Comprehend the Job Requirements: Understand the role you are applying for. Review the job description and identify the core skills. 
• Review Core Subjects: Refresh your knowledge of the fundamentals, such as the Node.js event loop, asynchronous programming, and Express.js. 
• Enhance Problem-Solving Abilities: Practice coding problems regularly. Platforms like upGrad offers a wealth of exercises tailored to Node.js, problem-solving, and algorithm design. 
• Prepare Responses for Behavioral Questions: Technical skills are important, but interviewers often look for cultural fit. Prepare answers for common behavioral questions, such as how you handle deadlines or challenges. 
• Stay Updated with Industry Trends: Node.js evolves rapidly. Keeping up with the latest advancements, libraries, and trends is crucial. Familiarize yourself with new features, performance optimizations, and integrations. 
• Rehearse for Interviews: Practicing mock interviews can help alleviate nerves. Rehearse explaining your thought process and technical concepts clearly. 
• Upgrade Skills with Courses: If you feel that there are areas of Node.js you need to strengthen, consider enrolling in specialized courses. 

By focusing on these strategies, you’ll be prepared for any Node.js interview questions, whether they're focused on core concepts, coding challenges, or behavioral assessments.

Also Read: Coding vs. Programming: A Never Ending Debate

Enhance Your Node JS Expertise with upGrad

As you prepare for Node.js interviews, it’s essential to continue enhancing your skills. upGrad offers a wide range of resources to deepen your Node.js expertise, equipping you with advanced knowledge that will make you stand out to employers. 

Below is a table that highlights certifications and courses that can help you sharpen your Node.js skills and prepare for your next job opportunity. 

Boost your career with our popular Software Engineering courses, offering hands-on training and expert guidance to turn you into a skilled software developer.

Master in-demand Software Development skills like coding, system design, DevOps, and agile methodologies to excel in today’s competitive tech industry.

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